A Dynamics Problem Regarding Friction.

In summary, the conversation discusses questions related to finding the coefficient of static friction between two masses and the time it takes for the top mass to fall off the bottom mass. The equations F=ma and fric = μ|Fn| are relevant to solving the problem. The attempted solution involves finding the acceleration of the 2kg mass relative to the ground and then realizing that the acceleration relative to the bottom mass is needed to answer the question.
  • #1
AvocadosNumber
16
0

Homework Statement



SSRnLDS.png


That was the given information. Here are the questions they ask, I have solved a) and b), but I am completely stuck on c). I'll just put them here in case information from them are necessary.

a) What is the coefficient of static friction between the 5.0 kg mass and the horizontal surface? (answer 0.33)

b) What is the coefficient of static friction between the two masses?

c) From the point when the top mass starts sliding how long will it take for the top mass to fall off the bottom mass? (0.97s)

Homework Equations



F=ma
fric = μ|Fn|

The Attempt at a Solution



Block on Top (2.0kg)
[tex]ƩFx=-fk[/tex]
[tex]ƩFx=-(0.3)(2kg*9.81m/s^2)[/tex]
[tex]ma=-(0.3)(2kg*9.81m/s^2)[/tex]
[tex]2kg*a=-5.886N[/tex]
[tex]a= \frac{-5.886N}{2kg}[/tex]
[tex]a= -2.943m/s^2[/tex]

then...
[tex]Δd=viΔt+\frac{1}{2}aΔt^2[/tex]
[tex]-1m=\frac{1}{2}2.943m/s^2*Δt^2[/tex]
[tex]-1m=-1.4715m/s^2*Δt^2[/tex]
[tex]-1m=-1.4715m/s^2*Δt^2[/tex]
[tex]\frac{-2m}{-1.4715m/s^2}=Δt^2[/tex]
[tex]Δt^2=0.68s^2[/tex]
[tex]Δt=0.82s[/tex]^Which is wrong =(
 
Last edited:
Physics news on Phys.org
  • #2
You've found the 2kg's acceleration relative to the ground (except, not sure why you have it as negative; isn't positive to the right?). Is that the acceleration you need to answer the question?
 
  • #3
So does that mean I need to find the acceleration relative to the bottom block?
 
  • #4
AvocadosNumber said:
So does that mean I need to find the acceleration relative to the bottom block?
You want the time it takes the top block to move 1m, starting from 'rest'. 1m relative to what? "rest" relative to what?
 
  • #5
Oh... I see now... relative to the bottom block.
 
  • #6
Quite so.
 

1. What is friction and how does it affect dynamics?

Friction is the force that opposes motion between two surfaces in contact. It can affect dynamics by reducing the speed and motion of objects, increasing energy loss, and causing wear and tear on surfaces.

2. How does the coefficient of friction impact a dynamics problem?

The coefficient of friction is a measure of the roughness or smoothness of two surfaces in contact. It affects a dynamics problem by determining the amount of force needed to overcome friction and the resulting motion of objects.

3. What are some common examples of friction in dynamics?

Some common examples of friction in dynamics include the rolling resistance of a car's tires on the road, the friction between a pitcher's hand and a baseball, and the friction between a ski and the snow.

4. How can friction be reduced in a dynamics problem?

Friction can be reduced in a dynamics problem by using lubricants, using smoother or more slippery surfaces, or by decreasing the force between the two surfaces in contact.

5. How does friction affect the accuracy of calculations in a dynamics problem?

Friction can affect the accuracy of calculations in a dynamics problem by introducing additional forces and energy losses that may not be accounted for. It is important to consider and accurately measure friction in order to make more precise calculations.

Similar threads

  • Introductory Physics Homework Help
Replies
13
Views
857
  • Introductory Physics Homework Help
Replies
14
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
6K
  • Introductory Physics Homework Help
Replies
5
Views
3K
  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Introductory Physics Homework Help
2
Replies
45
Views
5K
  • Introductory Physics Homework Help
Replies
1
Views
3K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
17
Views
13K
Back
Top